The present invention relates to a heat-sensitive recording paper which makes use of the color forming reaction of a colorless or pale-colored leuco dye with a color developing material, and more particularly to a heat-sensitive recording paper which is useful in producing a design drawing or usable as a master copy or a mother print for reproduction on a diazo type paper.
Heat-sensitive recording papers are well known which make use of the color forming reaction of a colorless or pale-colored leuco dye with a color developing material such that the two components are reacted by means of a thermal energy generated from a thermal head to produce a color image.
Since such heat-sensitive recording papers are relatively inexpensive and usable on a compact recording machine with an easy maintenance, the recording papers are not only used as recording media for facsimile machines, various computers or the like but also used for other various purposes.
Among such various purposes, three is a demand for heat-sensitive recording papers which are usable for producing design drawings or useful as a master copy for producing a copy on a diazo type paper (hereinafter called "diazo-copying"). To meet this demand, there have been developed heat-sensitive recording materials which have a support made of a transparent film or heat-sensitive recording materials which have a support made of a wood-free paper impregnated with a thermoplastic resin (Japanese Unexamined Patent Publications (Kokai) Nos. 53094/1981, 15013/1982, 103892/1982 and 108581/1986).
However, the heat-sensitive recording materials having as a support a film of a resin such as polypropylene, polyethylene terephthalate or the like are disadvantageous because the resin films used as a support are more expensive than papers, leading to increased production costs and because the films, when bent, tend to fog in the bent portion.
For use in producing a design drawing or a mother print (or a master copy) for producing diazo print, heat-sensitive recording papers are required to produce record images of high color density and to have an unrecorded portion of low opacity in order to form a sharp image in diazo print. When the recording paper has a support such as wood-free paper impregnated with a thermoplastic acrylic resin or the like, it is necessary to use a large amount of the resin to impart a high transparency. In this case, however, the recording paper disadvantageously shows lower image stability and has poor folding endurance so that it can not be stored as folded.